Generally, a construction machine, such as a hydraulic shovel, is provided with a counterweight used to maintain the balance of a machine body, for example, while the machine is operating. The counterweight is produced, for example, by filling the interior of a hollow outer shell made of sheet steel with a filler in which metal pieces (e.g., iron ore or iron pieces) used as weight materials are held together with cement or other materials.
Conventionally, the counterweight has been subjected to waste disposal after having been used. However, in recent years, an attempt to recycle the counterweight has been made in accordance with the promotion of recycling in many fields. In this case, a proposal has been made to recover the metal portion, which is great in specific gravity, from the used counterweight and then mix and use the metal portion with a filler of a new counterweight.
However, the counterweight and the recycling method have the following problems.
When a metal portion is recovered from a used counterweight by crushing and separating a filler into the metal portion and into the other filler portion, cement has easily been included in the metal portion. Therefore, cases have occurred in which the bulk specific gravity of recovered substances does not reach a given value, or the recovered substances do not have a bulk specific gravity usable as weight materials. Therefore, when such recovered substances are used to manufacture new counterweights, an operation to adjust the weight of each counterweight is needed, and, disadvantageously, much time is consumed because of low workability, thus raising manufacturing costs.
Additionally, when a brittle material like pig iron is used as a metal portion, the metal portion also is easily crushed in crushing a filler, and therefore the range of particle size distribution of the metal portion that has been recovered has had a tendency to be narrower than the range of the metal portion obtained when a new counterweight is manufactured. Hence, the bulk specific gravity of recovered substances becomes small, and cases have occurred in which the recovered substances do not have the bulk specific gravity usable as weight materials. Therefore, disadvantageously, much time is consumed because of low workability when new counterweights are manufactured, thus raising manufacturing costs.
Additionally, materials having low adsorptivity to a magnet are often contained in the metal portion, and therefore, when the metal portion is extracted from a used counterweight, a conventional drum-type magnetic separator of low peripheral speed/low magnetic force had the possibility that the recovered substances could not be easily separated from each other.
The invention has been made in consideration of the foregoing circumstances. It is therefore an object of the invention to provide a counterweight and a recycling method thereof capable of having excellent workability, capable of reducing manufacturing costs, and capable of achieving environmental conservation.